1. Technical Field
The present invention relates generally to cellular wireless communication systems; and more particularly to a method for distributing paging within such a cellular wireless communication system to reduce paging load by creating a plurality of location areas within the cellular wireless communication system such that registration requirements between the location areas are minimized.
2. Related Art
The cellular communications industry has experienced very rapid growth in both the areas serviced and the number of subscribers. In many metropolitan areas in North America, mobile switching centers receive service requests numbering in excess of 100,000 call attempts per hour from mobile units operating within respective service areas. The service area of each such mobile switching center typically includes a network of 100 or more cells. In its operation, the mobile switching center keeps track of all mobile units currently operating in its service area via a database commonly referred to as a visitor location register. The visitor location register stores information regarding the services available to each subscriber, his home mobile switching center and the current status (e.g., active or inactive) of the mobile unit.
The mobile switching center, however, does not usually have accurate information regarding the precise geographical location of each of the mobile units within the service area. Consequently, when a call is initiated to a mobile unit believed to be within the service area, a page must be broadcast over the forward control channels, which are also known as the paging and access channels of all cells in the service area. When the mobile unit responds to the page message, the particular cell containing the mobile unit is then identified from the reverse control channel used for the mobile response and the call is then set up. In the event there is no response to the page, the system assumes that the mobile unit is currently inactive and the call is treated accordingly.
Since each typical mobile switching center in an urban area serves a system with over 100 cells, in order to broadcast a page message over the forward control channels of all the cells in such a typical system, the paging message must be replicated a corresponding number of times and sent to each cell. As only one cell in the system can receive a response from the mobile unit, this means that a large number of these paging messages are an additional cost of locating the mobile unit but result in no reply whatsoever. System wide, each cell must send paging messages for every call initiated to every mobile unit operating within, or believed to be operating within, the service area. These paging messages put a huge load on the forward control channels of all cells in the service area consume resources of the mobile switching center that would otherwise be available for performing other tasks. Hence, the overall system performance is degraded by the overhead caused by the generation of unneeded paging messages.
Various approaches have been suggested for overcoming this problem. In one such approach, the service area of the cellular system is partitioned into location areas which are smaller than the service area. Every time a mobile unit enters a location area, it registers within the location update, such registration indicating that the mobile unit is operating within the location area. When a call is initiated to the mobile unit, therefore, the paging message is sent only from the cells making up the location area. Resultantly, the paging load across the system is dramatically reduced since each cell sends paging messages only for calls initiated to the mobile units registered within its location area. However, this approach does increase the number of registration activities as registration occurs each time an active mobile unit moves from one location area to another location. The registration activity in such a system is significantly greater than is required in systems where registration occurs only when a mobile unit is moved from one service area to another service area.
Setting location areas in a network, thus, is a trade off between paging and registration. First of all, location area size is an important factor in determining the location areas. If the location areas are too large, then the paging load on cells in the location areas will exceed the forward control channel link capacity. On the other hand, if the location areas are too small, the number of registrations introduced by setting the smaller location areas will consume the forward control channel link capacity. In both cases, active mobiles will be unable to receive calls and/or short message services due to the lack of forward link control channel capacity.
Thus, location area formation is far more complex than simply determining the size of the location areas. Due to the non-uniformity of traffic and mobility in wireless networks, the location of borders between location areas is a key factor in determining location area boundaries. Improper location area boundary settings may cause the network to perform more poorly than if no location areas were used at all.
Thus, there is a need in the art for an improved technique for determining location areas that will not only cause paging load to conform to limited control channel resources, but to cause registration operations to be minimized so that the capacity of a wireless communication system within which the location areas are implemented will be maximized.